609 research outputs found
Molecular Orbital Tomography Based on High-Order Harmonic Generation: Principles and Perspectives
No full textGeneration of ultrashort pulses by four wave mixing in a gas-filled hollow core fiber
No full textThe four wave mixing (FWM) process is widely exploited for the generation of tunable ultrashort light pulses. Usually this process is driven in bulk materials, which are however prone to optical damage at high pump laser intensities. A tunable source of ultrashort 10 mu J level pulses in the visible spectral region is described here. In particular, we report on the implementation of FWM driven by a two-color ultrafast laser pulse inside a gas-filled hollow core fiber (HCF). Due to the high-damage threshold and the long interaction distance, the HCF-based FWM configuration proves to be suitable for high-energy applications. Moreover, this technique can be potentially used for ultrashort pulses generation within a wide range of spectral regions; a discussion on the possibility to extend our scheme to the generation of few-cycle mid-IR pulse is provided
High-order harmonic generation in a microfluidic glass device
No full textWe report on the efficient generation of high-order harmonics in helium gas inside complex glass micro-devices fabricated by femtosecond laser micromachining. By exploiting the three-dimensional capabilities and extreme flexibility of this fabrication technique we developed fluidic micro-structures in a fused-silica substrate that allowed us to achieve accurate control of the gas density inside a micrometer-sized microchannel. As a result, we achieved a broadband spectrum of extreme ultraviolet (XUV) radiation which extends up to 200 eV and we observed a considerable increase in the harmonics generation efficiency if compared with traditional harmonic generation in gas jets. We foresee that the application of femosecond-laser-micromachined glass devices to high-order harmonics generation can be extended to more complex on-chip systems including different functionalities, thus opening the possibility to future miniaturization of XUV and Attosecond beamlines
Optical parametric amplification techniques for the generation of high-energy few-optical-cycles IR pulses for strong field applications
No full textOver the last few decades, the investigation of ultrafast phenomena occurring in atoms, molecules and solid-state systems under a strong-field regime of light-matter interaction has attracted great attention. The increasing request for a suitable optical technology is significantly boosting the development of powerful ultrafast laser sources. In this framework, Optical Parametric Amplification (OPA) is currently becoming a leading solution for applications in high-power ultra-broadband light burst generation. The main advantage provided by the OPA scheme consists of the possibility of exploring spectral ranges that are inaccessible by other laser technologies, as the InfraRed (IR) window. In this paper, we will give an overview on recent progress in the development of high-power few-optical-cycle parametric amplifiers in the near-IR and in the mid-IR spectral domain. In particular, the design of the most advanced OPA implementations is provided, containing a discussion on the key technical aspects. In addition, a review on their application to the study of strong-field ultrafast physical processes is reported
Development of ultrafast Mid-IR sources and their applications to high-order harmonic generation spectroscopy
No full textLa generazione di armoniche di ordine elevato (HHG) è un effetto non lineare che si verifica in caso di interazione di impulsi ultracorti con campioni atomici o solidi. La generazione di armoniche nel caso atomico è ben consolidata e costituisce la base della scienza agli attosecondi. Il processo non lineare avviato dalla ionizzazione tunnel e completato dalla ricombinazione dell'elettrone ionizzato con il suo ione parente codifica numerose informazioni sulla struttura interna del campione in esame. In questo contesto, abbiamo sviluppato una tecnica per la ricostruzione dell'orbitale molecolare più esterno di una molecola. La tecnica prevede l'utilizzo di un primo impulso laser che permette di allineare le molecole nello spazio e di un secondo impulso per generare gli spettri di armoniche necessari alla ricostruzione dell'orbitale. In questo contesto, verrano mostrati i risultati ottenuti nella molecola di CO2.
Nel caso dei solidi, l'osservazione di armoniche di ordine elevato costituisce uno degli ambiti di frontiera della scienza ultraveloce e agli attosecondi. Lo sviluppo di impulsi intensi a medio infrarosso ha aperto recentemente l'indagine sperimentale del processo HHG nei semiconduttori. Nei solidi, in analogia con il caso atomico, l'emissione di armoniche ha origine dal processo di ricombinazione degli elettroni con le lacune associate. Queste coppie elettrone-lacuna vengono generate a seguito del processo di ionizzazione tunnel, e la loro propagazione prima della ricombinazione produce due correnti indipendenti nelle bande di valenza e conduzione del semiconduttore. La seconda parte di questa tesi mira ad approfondire questo processo. Verranno introdotti i fondamenti che regolano i fenomeni di campo forte a seguito dell'interazione laser-materia in sistemi periodici (materiali semiconduttori) a confronto con il caso atomico. Verranno poi discussi i risultati sperimentali ottenuti in cristalli di seleniuro di diamante e zinco.High-order harmonic generation (HHG) is a nonlinear effect occurring upon interaction of intense ultrashort pulses with atomic or solid targets. Harmonic generation in the atomic case has been well established and has formed the basis of attosecond science. The nonlinear process initiated by tunnel ionization and completed by the recombination of the ionized electron with its parent ion encodes needed information regarding the intimate structure of the species under consideration. In this framework, we have developed a technique for the tomographic reconstruction of the Highest Occupied Molecular Orbital of a molecule, in which a laser pulse aligns the molecule in space, and another one generates the harmonic spectra needed for the reconstruction. In this context, we performed experiments for the tomographic reconstruction of the CO2 molecule. In the case of solids, the advent of potential mid-infrared pulses has opened up the experimental investigation of HHG process in semiconductors. In solids, harmonic emission originates from the recollision of electrons with their associated holes, similarly to atomic case, while tunnel ionization is termed as excitation of electron-hole pairs that accelerate within the material. The second part of the thesis aims at providing this insight. An introduction to the basic foundation of HHG in solids along with comparison to the atomic case is discussed. This will be followed by an experimental demonstration of HHG from Diamond and Zinc Selenide crystals.DIPARTIMENTO DI FISICA31DE SILVESTRI, SANDROFINAZZI, MARC
High-order harmonic generation in femtosecond laser micromachined devices
No full textWe demonstrate the generation of high-order harmonics in a fused-silica device fabricated through femtosecond laser micromachining. This achievement paves the way for the miniaturization of HHG applications from large-scale laboratories to microstructures
High-order harmonic generation spectroscopy by recolliding electron caustics
No full textSpectral focusing of the recolliding electron in high-order harmonic generation driven by two-color fields is shown to be a powerful tool for isolating and enhancing hidden spectral features of the target under study. In previous works we used this technique for probing multi-electron effects in xenon and we compared our experimental results with time-dependent configuration-interaction singles calculations. We demonstrate here that this technique can be exploited for reconstructing the enhancement factor of the xenon giant dipole resonance and we discuss the sensitivity of this method to macroscopic effects. We then extend the technique to argon in order to test the applicability of this procedure to other targets
Dentigerous Cyst
No full textDentigerous Cyst
Dental School Radiology Presentation : Dentigerous Cyst
Author : Tadinada, Aditya
Medical Subject : Dentigerous Cyst, Odontogenic Cysts
Clinical Presentation Description : Radiolucency arising from the CEJ of an unerupted tooth
Location of Abnormality : Posterior Mandible
Radiological Features : Radiolucency arising from the CEJ of an unerupted tooth
DDx Description : Dentigerous cyst, odontogenic keratocyst, ameloblastoma
Type of Image : Panoramic Radiograph
Digital Publisher : UCONN Health Center : Kilham, Jessica
Format : jpg
Date : 201
Design, modeling and real-time monitoring of continuous powder mixing processes
No full textContinuous processing is an advantageous alternative for the current methods used in the pharmaceutical manufacturing. Important advantages that it offers include smaller equipment footprint, reduced efforts in the scale-up work, and the potential to utilize already continuous processes to make the entire manufacturing more efficient. In the current pharmaceutical manufacturing environment, powder mixing process is carried out in the batch mode. The necessary methods and guidelines to design an equivalent continuous process are not well established. The work presented in this dissertation focuses on the characterization, design and optimization of a continuous powder mixing process for pharmaceutical powders. A systematic study was performed of the effects of process and design variables, and material properties involved in the continuous powder mixing process. The bulk powder flow behavior was characterized using the residence time distribution (RTD) measurement approach. Impeller speed, material bulk density and impeller design greatly influenced the mean residence time. With increasing impeller speed, mechanical fluidization was observed, which significantly affected axial dispersion coefficients. Intermediate rotation rates exerted maximum strain on the material, which leads to maximum homogenization. The strain measurements correlated well with the properties of tablets including content uniformity and tablet hardness. Mixing performance was largely dominated by the material properties of the mixture, and the blend uniformity measurement was affected by the sample size analyzed. An experimental protocol was developed to measure the blend uniformity in the in-line mode, and a methodology was further built to quantitatively relate the in-line NIR measurements with the off-line wet chemistry measurements. Considering the shear limitations of the continuous bladed mixer, alternative blending strategies, suitable for blending of cohesive materials were also demonstrated. A combination of a high-shear mixing followed by a low-shear mixing process provided the optimal mixing performance. The predictive understanding of the continuous powder mixing process developed in this dissertation can assist towards the design and development of a fully controlled continuous manufacturing process.Ph. D.Includes bibliographical referencesIncludes vitaby Aditya U. Vanaras
Tunable, Few-Cycle, CEP-Stable Mid-IR Optical Parametric Amplifier for Strong-Field Applications
No full textWe present a robust, three-stage optical parametric amplifier driven by a Ti:Sapphire ultrafast laser system that implements passive carrier-envelope phase stabilization and directly generates five-cycle mid-IR pulses by dispersion compensation. The source is based on potassium titanyl arsenate crystals and exploits intra-pulse difference-frequency seed generation in the mid-IR. This source will be particularly suited for applications in strong-field physics, such as high order harmonic generation and photoelectron spectroscopy
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